1. Field of the Invention
Various aspects of the present invention relate to a middle phase type continuously variable valve timing system (hereinafter, referred to as middle phase type CVVT), and more particularly, to a middle phase type continuously variable timing system using an electronic active lock pin control method which may improve target trackability of the middle phase type CVVT to a general CVVT engine level by performing lock pin unlocking and a phase control while generating a middle phase type CVVT target value.
2. Description of Related Art
Generally, middle phase type CVVT has rapider system responsiveness and a wider use area of a cam as compared with CVVT, by controlling a position of a cam at a middle position, not at a most retarded angle (intake) position and a most advanced angle (exhaust) position, when the middle phase type CVVT performs a control based on a difference between a target value and a current value of the cam, thereby improving the system responsiveness and fuel efficiency and reducing exhaust gas more than the CVVT.
In particular, the middle phase type CVVT uses an oil-flow control valve (OCV) which is installed at a lock pin side channel for a CVVT rotor which restricts a lock pin at the most advanced angle and the most retarded angle and a middle phase type oil-flow control valve (OCV) for a lock pin unlocking channel which unlocks the lock pin at the middle phase, thereby returning a mechanical default position based on a limphome mode while releasing an electronic lock pin by turning on/off a valve. Here, the limphome is a safe function of implementing minimum driving of a vehicle even when a problem of performance and a sensor operation arises.
However, the lock pin of the middle phase type CVVT controls an engine electronic control unit (ECU) using an electrical signal of the middle phase type OCV and thus needs a physical unlocking time after an electrical signal is applied to the valve and before the lock pin is unlocked.
Therefore, the middle phase type CVVT is first operated by supplying oil to the lock pin side channel of the middle phase type CVVT before the lock pin is unlocked, which generates a side-force of the rotor and the lock pin to lock the lock pin, thereby causing a physical lock-in phenomenon to prevent the lock pin from being unlocked.
In particular, the lock pin unlocking delay is developed to become a cam oscillation phenomenon of the middle phase type CVVT. Further, when the unlocking of the lock pin is not permitted, the middle phase type CVVT operation is not permitted, and as a result, drivability may deteriorate and an engine may stall.
An adverse effect due to the lock pin unlocking delay may be improved by performing a middle CVVT assist control for side-force offset after the lock pin is unlocked and then performing the middle phase type CVVT phase control, but a delay time from a timing at which the target value of the CVVT is generated to a timing at which the CVVT moves occurs at the middle phase type CVVT, and thus a reduction in power performance may not be completely solved.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.